The invention relates to the field of surgically implantable devices and methods in the biomedical field. Implantable cuffs have been used for the stimulation and recording of biological tissues, particularly nerves. Stimulation of the nervous system with nerve cuffs can result in recovery of lost sensory or motor function in individuals with neurological deficits. An example of such an application is the Freehand™stimulator (Neurocontrol Corporation, Ohio, USA) that can restore a degree of hand function in an individual with a spinal cord injury. Recording has also been performed with implantable cuffs. Recording nerve function can relay vital information back to a processor that assists in decision-making based on the activity of the nerve. For example, in sleep apnea, patients implanted with nerve cuffs rely on the nerve cuff to be used for recording as well as stimulation when necessary. By targeting a nerve with an implanted nerve cuff, much less electrical current is required than for intra-muscular stimulation or surface stimulation. Intramuscular stimulation involves using an electrode directly in the muscle, whereas surface stimulation utilizes electrodes at the skin surface to activate nerves in the general area of interest. Surface stimulation is much less selective of the muscles it can stimulate as compared to nerve cuffs.
Most implantable electro-neuroprosthetics that target peripheral nerves use some type of nerve cuff. Currently there are three primary types of nerve cuffs used to stimulate nerves with an electro-neuroprosthesis, namely C-shaped cuffs, helical cuffs, and nerve reshaping cuffs.
C-shaped nerve cuff electrodes are named for their c-shaped cross section. They range from split cylinder, spiral and multi-compartmental designs. An example is seen in U.S. Pat. No. 6,600,956 to Maschino et al. Generally the cuff is made of an electrically insulative substrate with one or more imbedded electrically conductive elements designed to interact electrically with the nerve. The preferred substrate is biocompatible, the most common material being silicone rubber. The main draw back to c-shaped nerve cuffs is that the internal diameter of the nerve cuff needs to be estimated prior to the surgery, and hence it can result in loose fitting cuffs if made too large, or too constricting cuffs resulting in nerve damage if made too small. This can greatly increase costs as multiple sizes need to be made available to the surgeon to minimize problems. Spiral electrodes that are self curling alleviate the size problem and can be removed with minimal force.
Helical cuffs such as shown in U.S. Pat. No. 5,964,702 to Grill et al. are built much like spiral cuffs from a self curling substrate, but they are cut to look like a spring. One main draw back is that they need to be wrapped around the nerve, which can be a time consuming process. Furthermore, helical cuffs rely entirely on the substrate properties to close properly as there is no closing mechanism. This can result in inappropriate contacts being made to the nerve. Helical cuffs are also susceptible to size constraints.
Nerve reshaping cuffs reshape the nerve to fit the cuff's internal space. An example of a nerve reshaping cuff is illustrated in U.S. Pat. No. 5,634,462 to Tyler et al. This type of cuff relies on a force being applied to the nerve itself to squeeze it into a desired shape, either by using rigid structures or corrugations in the nerve cuff. If appropriate pressure is used, and enough space provided for the nerve, there is a possibility of using multiple electrically conductive units to isolate and stimulate only certain parts of the nerve. However, one risk is that damage to the nerve can occur during the installation. As well, a possible tensile strength decrease can weaken the nerve. In the case of large rigid structures near the nerve there is a further risk for increasing the incidence of inflammation in response to the mechanical aggravation of the tissues. The rigidity needed to shape the nerve in a corrugated nerve cuff such as in U.S. Pat. No. 5,634,462 also limits the ability of the cuff to accommodate different nerve sizes, so as above, different size cuffs must be provided for different nerve sizes. Adjusting the cuff intra-operatively to re-position conductive elements, or to adjust for size, is resisted by the design and rigidity of the structure. Finally, the corrugations of this type of device are designed to minimize contact points with the nerve, which for some applications limits the nerve surface which can be directly contacted with electrical contacts of nerve interacting devices.
In spite of the large number of available nerve cuff designs, there remains a need for an adjustable size tissue cuff, that can be quickly installed, intra-operatively adjusted, and which places just the right amount of pressure on the nerve or tissue to allow for ideal contact with conductive units without damaging the nerve. As well, given the many different functional electrical devices currently available that rely on peripheral nerve stimulation, there is a further need for a nerve cuff that is not limited to a single type of electrode lead design.